B9. -16- 7 API Figure B9 shows two point charges, charge 1 (qi-+2 nC) and charge 2 (q2=-8 nC) are placed at position A and position B, respectively. Both charges are fixed. 12 cm Вст Figure B9 (a) Find the total electric field E at position O. 0 8cm 8cm B Вст 4-C (c) (b) Find the electric potential V at O (assume V - 0 at infinity). (3 marks) (2 marks) How much is the work done if we bring a particle of charge 3 (q3=+3 nC) from infinity to O? (1 mark) (d) Determine the magnitude of force acting on charge 3 by charges 1 and 2. (I mark)